Heretofore proposed resins for coating compositions are divided, from the morphological point of view, into three classes, i.e. soluble type resins (including a water soluble resin), colloidal dispersion resins and granular resins. A soluble type resin is very useful for coating purpose because of its capabilities to act as a binder as well as a pigment dispersing agent and its excellent film-forming property. Therefore, such a resin has been practically and widely used as a resinous vehicle for an oil paint. However, with the increased demands for such social needs as economization of natural resources, energy-saving and conservation of good surroundings, the use of oil paints is decreasing and public attentions are mostly directed to the use of high quality aqueous paints, high solids coating compositions and powder paints, in place of the oil paints. Neverthless, a soluble type resin is hardly applicable to such paints because of its comparatively poor application characteristic and insufficient film performance. Colloidal dispersion resins had once been tried for use in aqueous paints, and however, the application characteristics and the stabilities of the paints were not yet up to the mark and such resins had failed to be the main current of the resinous vehicles of the coating compositions.
Granular resins are supplied in the forms of emulsions, microgels, non-aqueous dispersions and powder resins, and have been watched with keen interest in paint industries, because of their capabilities of resulting ideal aqueous paints, high solids paints and powder paints which may fulfill the requirements of economization of natural resources, energy-saving and conservation of good surroundings.
They are used singularly or in combination form with other soluble type resins and are believed to act as a binder, a rheology regulator or a polymer filler. Thus, a high quality film can be obtained therewith.
However, when the granular resin is used alone, it is unable to get a uniform or excellent film and the resulting film has a serious drawback of being deficient in film appearance. Even when the granular resin is combined with a soluble type resin, there is a case wherein the viscosity of the combined system is greatly increased as compared with that of the soluble type resin alone due to the considerable interaction between the surfaces of granules and soluble type resin. Therefore, a great care is often required in the actual use of such combined resins.
An object of the invention is, therefore, to provide novel composite resin particles which are free from the drawbacks of the abovementioned coating use resins.
Additional objects of the invention are to provide novel composite resin particles which are able to be used either singularly or in combination form with any other resins customarily used in paint industry, to give excellent coating compositions with good application characteristics and storage slability, and capable of giving a uniform film with an excellent appearance, and a dispersion composition comprising said resin particles and an organic solvent.
The present inventors have now found that the composite resin particles each of which comprises a crosslinked granular body portion and a number of linear polymer chains, a part of the respective chains penetrating into the inside of said granular body portion and the remaining part extending outwardly therefrom, are quite useful in paint industries because of having comparatively lower solution viscosities, capability of forming a uniform coating, and being excellent in compatibility with other resins, and on the basis of these findings, the inventors have succeeded in coming to the present invention.
Thus, according to the present invention, there are provided composite resin particles each of which comprises a granular body portion of a crosslinked polymer having a mean diameter of 0.01 to 10.mu., and a number of linear polymer chains, a part of the respective chains penetrating into said body portion and the remaining part extending outwardly therefrom, the process for the preparation of such particles and a resinous composition for coating use containing the same.
The novel composite resin particles of the present invention are characterized in that each particle comprises a granular body portion of a crosslinked polymer and a number of linear polymer chains and has a larger grain size as compared with that of the original particle of the crosslinked polymer, the grain size being at most 2.5 times the original size of said crosslinked polymer particle.
Also, the solution viscosity of the resinous composition is significantly lower as compared with that of the mere blend of the cross-linked polymer particles and the linear polymer concerned.
The granular body portion is composed of a crosslinked polymer and has a mean diameter of 0.01 to 10.mu., the polymer being of polycondensation type as polyester resin, epoxy resin and amino resin or of addition polymerization type as acrylic resin and vinyl resin. Such resin particles may be advantageously prepared by any of the known processes as, for example, an emulsion polymerization, a non-aqueous dispersion polymerization or a solution polymerization, and the product may be, according to the method of preparation, used as it is, or after separation and pulverization as desired.
The linear polymer chain is characterized by being composed of a linear polymer prepared by the addition polymerization of (a) polymerizable ethylenic compound(s). Examples of such polymerizable ethylenic compounds are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and their esters, styrene, vinyl toluene, acrylonitrile, vinyl acetate, acrylamide, N-methylol acrylamide and other similar monomers.
Employable acrylic or methacrylic esters may be represented by the formula: ##STR1## wherein R.sub.1 is H or CH.sub.3 and R.sub.2 is a saturated hydrocarbon having 1 to 15 carbon atoms, including methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, lauryl acrylate, lauryl methacrylate and the like. Other esters may include the members represented by the abovesaid formula wherein R.sub.2 is a saturated hydrocarbon bearing hydroxyl group. Examples of such members are hydroxy propyl acrylate, hydroxy propyl methacrylate, 2-hydroxy ethyl acrylate, and 2hydroxy ethyl methacrylate.
The present composite resin particles are, as already stated, characterized in that each particle has a specific structure such that a part of the respective linear chain penetrates into the inside of the crosslinked polymer particle and the remaining parts extend outwardly therefrom.
Such composite resin particles may be easily and advantageously prepared by the method wherein addition polymerizable ethylenic compound(s) is (are) polymerized by a solution polymerization in the presence of crosslinked polymer particles.
That is, any of the known solution polymerization techniques may be advantageously used as, for example, by adding into a reaction vessel a radical polymerization initiator (e.g. organic peroxide or organic azo compound), solvent(s), crosslinked polymer particles and polymerizable monomer(s) and heating the mixture to effect polymerization, or by placing, in a reaction vessel, organic solvents and adding, under heating, dropwise a polymerization initiator, crosslinked polymer particles and monomers, or by the combination of said techniques.
The present composite resin particles are, owing to the specific preparation method used, characterized by having the specific structure of the so-called semi-interpenetrating polymer network, wherein a part of the respective polymer chain penetrates into the inside of the crosslinked polymer particle and the remaining part extends outwardly therefrom. The said composite resin particles are strictly distingushed from the mere blend of crosslinked polymer particles and linear polymer, in which case a number of linear polymer chains are merely attached to the respective crosslinked polymer particle, in respect of, inter alia, viscosity behavior or the like.
Though the weight ratio of crosslinked polymer/linear polymer in the present composite resin particle may considerably vary with the intended use, the kind of polymer and the like, it is generally determined in a range of 100 parts by weight of the crosslinked polymer/5 to 1000 parts by weight of the linear polymer.
It is, of course, possible to increase or decrease the amount of the linear polymer than the abovesaid range. The present composite resin particles are, after being dispersed in an organic solvent, used in a paint industry. As the organic solvent, any of the members customarily used in coating compositions may satisfactorily be used, including aromatic hydrocarbons (e.g. toluene, xylene), aliphatic hydrocarbons, alcohols, ethers, esters, ketones and the like. The thus obtained dispersions may be used as they are or in combination with the other resinous vehicles, in either conventional or novel type coating compositions.
In the present invention, crosslinked polymer particles and linear polymer are closely bound together by the adoption of solution polymerization technique, thereby forming composite resin particles of the novel structure hereinbefore stated. The inventors have also succeeded in having a novel coating composition with said resin particles, which has excellent properties in regard to viscosity, film appearance, application characteristic, stability and film-forming property.
The invention shall be now more fully explained in the following examples. Unless otherwise being stated, all parts are by weight.